1. Field of the Invention
The present invention relates to a wireless communication device, which adopts the spread spectrum (it will be hereinafter abbreviated as “SS”) scheme in order to operate in weak radio waves and, more particularly, to a signal processing unit and a wireless communication device, which are able to detect a frequency in a short time by the use of a small-scale operation circuit when performing correlation detection.
2. Description of the Related Art
[Bidirectional Wireless System: FIG. 12]
A wireless communication device that has been conventionally used in a bidirectional wireless system adopts a spread spectrum scheme to operate in weak radio waves.
The conventional bidirectional wireless system will be described with reference to FIG. 12. FIG. 12 is a schematic diagram illustrating the conventional bidirectional wireless system.
The conventional bidirectional wireless system is provided with a wireless communication device as a base station 1 which has a transmitting unit 1a and a receiving unit 1b, and a wireless communication device as a portable equipment 2 which has a transmitting unit 2a and a receiving unit 2b. The conventional bidirectional wireless system transmits operation commands from the portable equipment 2 to the base station 1 by operating an input device of the portable equipment 2, so that the base station 1 is operated according to the commands.
The base station 1 is to transmit responses to transmission states of the commands or state information of the base station 1 to the portable equipment 2.
That is, the conventional bidirectional wireless system is a weak wireless system capable of performing bidirectional communication (half duplex) adopting the SS.
In the bidirectional wireless system, the portable equipment 2 plays a leading role in operation. The base station 1 receives the commands from the portable equipment 2 by intermittently receiving the transmission from the portable equipment 2, and the portable equipment 2 is put into an operation mode only when it is to be operated. Therefore, it is possible to significantly reduced power consumption.
[Configuration of Conventional Signal Processing Unit: FIG. 13]
A signal processing unit in the wireless communication device will be described with reference to FIG. 13. FIG. 13 is a block diagram illustrating a configuration of a conventional signal processing unit.
The conventional signal processing unit is provided with an ADC (Analog Digital Converter) control unit 11, an AGC (Auto Gain Control) unit 12, APC/AFC (Auto Power Control/Auto Frequency Control) control unit 13, a DAC (Digital Analog Converter) control unit 14, a carrier demodulating unit 15, a carrier data generating unit 16, a carrier modulating unit 17, a receiving data decoding unit 18′, a spread code generating unit 20′, a spread modulating unit 21′, a correlation peak detecting unit 22′, a coarse frequency deviation detecting unit 23′, and a fine frequency deviation detecting unit 24′.
Parts of the conventional signal processing unit will now be described in detail.
The ADC control unit 11 performs control to generate a control signal for the A/D converter (designated as “A/D”), and to receive a receiving IF (Intermediate Frequency) signal as an input signal from the A/D converter.
The AGC unit 12 controls a gain control signal which is outputted to the AGC amplifier in a wireless communication unit, so that the receiving IF signal output coming from the ADC control unit 11 may always be kept to have a predetermined amplitude.
The APC/AFC control unit 13 receives, as an input thereto, the control signal for monitoring temperature of the wireless communication unit from the A/D converter using a thermistor, and outputs an AFC correction value and an APC correction value to the carrier data generating unit 16 and the carrier modulating unit 17, respectively, with respect to the monitored value.
The DAC control unit 14 delivers data, which is modulated in carrier by the carrier modulating unit 17, to the D/A converter.
The carrier demodulating unit 15 performs a processing of removal of an IF carrier component with respect to the receiving IF signal which is outputted from the ADC control unit 11 and further a down sample processing on the afore-processed signal, and then outputs the eventual signal to the receiving data decoding unit 18′, the correlation peak detecting unit 22′, and the coarse frequency deviation detecting unit 23′, respectively.
The carrier data generating unit 16 performs a frequency correction processing according to a frequency deviation value or the like from the coarse frequency deviation detecting unit 23′ and the fine frequency deviation detecting unit 24′, and generates IF carrier data to be supplied to the carrier demodulating unit 15 and the carrier modulating unit 17.
The carrier modulating unit 17 performs an APC correction processing according to an APC correction request from the APC/AFC control unit 13, with respect to the IF carrier data which is supplied from the carrier data generating unit 16, and also performs the carrier modulation processing with the IF carrier data, with respect to spread modulation processing data which is input from the spread modulating unit 21′.
The receiving data decoding unit 18′ detects a synchronizing word after performing a fine frequency correction of a synchronized IF carrier frequency, and performs a demodulation processing of user data.
The spread code generating unit 20′ generates a spread code which is used in performance of a spread modulation and a despread processing. At this stage, two types of spread codes are necessary to be used for synchronizing word/REF (Reference) data and for the user data.
The spread modulating unit 21′ performs a differentially-encoding processing of the synchronizing word/REF data and the spread modulation processing of the transmission user data and the synchronizing word/REF data after being differentially encoded.
The correlation peak detecting unit 22′ performs a correlation processing on a carrier demodulated data which is outputted from the carrier demodulating unit 15 to perform a correlation peak detection.
The coarse frequency deviation detecting unit 23′ detects residual frequency components according to an IF carrier frequency deviation amount between the base station and the portable equipment on the carrier demodulated data which is outputted from the carrier demodulating unit 15, and outputs the frequency deviation amount to the carrier data generating unit 16.
The fine frequency deviation detecting unit 24′ performs frequency detection at a high accuracy on the correlation data of which a peak has been detected, in order to further decrease the frequency deviation amount, and outputs the fine frequency deviation amount to the carrier data generating unit 16.
In addition, as a relevant prior art, there is a JP-A-2004-214960 (Patent Document 1).
The Patent Document 1 discloses an OFDM demodulating apparatus in which a peak detection circuit accumulates guard correlation signals at a period of the predetermined number of symbols to generate an accumulation signal from which a peak timing is detected, and calculates a phase component of the guard correlation signal in the peak timing once as per one symbol, thereby correcting a deviation amount of a center frequency of OFDM signals.
Nevertheless, in the signal processing unit according to the conventional wireless communication device, when performing the correlation detection, it is requested that the detection accuracy of the coarse frequency deviation detecting unit should be 32 Hz.
In order to realize the detection accuracy of 32 Hz, it is necessary that either FFT (Fast Fourier Transform) operation processing points are set to 1,024 points from 32 points of the said signal processing unit or FFT operation sampling intervals are set to 1/1,024 sec from 1/32,768 sec of the said signal processing unit.
When the operation sampling interval is set to be longer, even frequency deviation components of equal to or more than 512 Hz (Nyquist frequency) must be also considered as frequency components of equal to or less than 512 Hz. Therefore, no normal frequency detection can be performed. That is to say, there occurs such a problem that the detectable range of frequencies must be restricted.
On the other hand, when the operation processing point is set to be 1,024 points, there is a problem such that an extensive increase in the operation processing time and the operation processing circuit must be brought about.